Is Feynman's QFT Unitarity Issue Resolved?

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Feynman's work on electrodynamics highlighted a significant issue with unitarity in quantum field theory (QFT), where the sum of probabilities did not equal unity due to the replacement of the delta function with a broader function. This deviation was minimal when the width was small, suggesting that renormalization could address the issue. However, Feynman noted he could not conclusively demonstrate that the apparent violation of unitarity was resolved. In response to inquiries about the current status, it was confirmed that modern renormalized perturbation theory has successfully preserved unitarity. The discussion indicates that the unitarity issue in Feynman's QFT has indeed been resolved through advancements in theoretical physics.
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From Richard Feynman's Nobel Prize Speech.

It must be clearly understood that in all this work, I was representing the conventional electrodynamics with retarded interaction, and not my half-advanced and half-retarded theory corresponding to (1). I merely use (1) to guess at forms. And, one of the forms I guessed at corresponded to changing d [delta function] to a function f of width a2, so that I could calculate finite results for all of the problems. This brings me to the second thing that was missing when I published the paper, an unresolved difficulty. With d replaced by f the calculations would give results which were not "unitary", that is, for which the sum of the probabilities of all alternatives was not unity. The deviation from unity was very small, in practice, if a was very small. In the limit that I took a very tiny, it might not make any difference. And, so the process of the renormalization could be made, you could calculate everything in terms of the experimental mass and then take the limit and the apparent difficulty that the unitary is violated temporarily seems to disappear. I was unable to demonstrate that, as a matter of fact, it does.​

Does anyone know whether this difficulty has been resolved?
 
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PatrickPowers said:
Does anyone know whether this difficulty has been resolved?
Yes, a long time ago. Modern renormalised perturbation theory has been shown to
preserve unitarity.
 
Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?

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